Update core/src/main/resources/lib/layout/skeleton.jelly

Co-authored-by: Alexander Brandes <brandes.alexander@web.de>

Author: krisstern

core/src/main/resources/lib/layout/skeleton.jelly

@@ -25,7 +25,7 @@ THE SOFTWARE.
 <?jelly escape-by-default='true'?>
 <j:jelly xmlns:j="jelly:core" xmlns:st="jelly:stapler">
   <st:documentation>
-    <st:attribute name="type" use="optional">
+    <st:attribute name="type" use="optional" since="TODO">
       The type of skeleton, available options are 'form' and 'side-panel'.
 
       Defaults to 'form'.